Integrins are non-covalently linked α/β heterodimeric receptors that mediate cell adhesion, migration and signaling. Together with their ligands, integrins play central roles in many processes including development, hemostasis, inflammation and immunity, and in pathologic conditions such as cancer invasion and cardiovascular disease. Leukocyte migration and recruitment is essential for their normal immune response to injury and infection and in various inflammatory and autoimmune disorders [1]. For example, in response to injury or infection leukocytes are recruited into the tissues where they participate in immune clearance [2]. The β2 integrins, a sub-family of α/β heterodimeric integrin receptors that have a common β-subunit (β2, CD18) but distinct α-subunits (CD11a, CD11b, CD11c and CD11d [3]), are leukocyte specific receptors [4]. β2 integrins, including highly expressed integrin CD11b/CD18 (also known as Mac-1, CR3 and αMβ2), modulate leukocyte functions, including cell adhesion, migration, recruitment and activation [2]. CD11b/CD18 recognizes the complement fragment iC3b, Fibrinogen, and ICAM-1 as ligands, among various others. CD11b/CD18 has been implicated in many inflammatory and autoimmune diseases, such as ischemia-reperfusion injury (including acute renal failure and atherosclerosis), tissue damage, stroke, neointimal thickening in response to vascular injury and the resolution of inflammatory processes [5-9]. Leukocytic β2 integrins also modulate tumor infiltration. For example, tumors also secrete inflammatory cytokines to recruit CD11b-expressing myeloid cells to facilitate neovascularization [10]. During cancer treatments, irradiated tumors recruit large numbers of specific leukocytes, bone marrow-derived CD11b-expressing myeloid cells expressing matrix metalloproteinase-9 (MMP-9), that restore tumor vasculature and allow tumor re-growth and recurrence [11]. Recent studies have shown that treatment with CD11b antagonists (anti-CD11b antibody) reduces CD11b-expressing myeloid cell infiltration and an enhancement of tumor response to radiation in mice [11]. Additionally, inflammatory leukocytes potentiate anti-GBM nephritis. Experimental anti-GBM nephritis in mice is a model of rapidly progressive glomerulonephritis, is characterized by proteinuria, leukocyte infiltration and glomerular crescent formation [12, 13]. Leukocytes play a critical role in the pathogenesis of anti-GBM nephritis, and their number correlates with the percentage of crescentic glomeruli. CD11b−/− animals show no proteinurea and strong protection of renal function [14], suggesting that agents targeting this integrin have a potential to treat this disease.
In addition to increasing cell adhesion and modulating migration, the beta2 integrins, including CD11b/CD18, mediate a number of intracellular signaling events, including production of reactive oxygen species and modulation of a number of pro- and anti-inflammatory genes in inflammatory cells [15-20]. Integrin activation and ligand binding leads to its clustering on the cell surface and initiates outside-in signaling, including the activation of PI3-K/Akt and MAPK/ERK1/2 pathways [16, 21], thereby mimicking the anchorage-dependent pro-survival signals in most cells. Ligation and clustering of integrins also synergistically potentiates intracellular signaling by other receptors (such as, Toll-like receptors (TLRs) and cytokine receptors interleukin-1 receptor (IL-1R) and TNFR) and both induce transcription factor (such as, NF-κB) dependent expression of pro-inflammatory cytokines (e.g.; IL1β, IL6, TNFα) as well as release of other factors (e.g.; Tissue Factor).
Thus, there is a considerable potential for agents that modulate the function of CD11b/CD18 and other beta2 integrin as therapeutic agents for the treatment of various diseases and conditions, including inflammatory conditions. Indeed, blocking beta2 integrins, including CD11b/CD18, and their ligands with antibodies and ligand mimics (anti-adhesion therapy) [22-24] and genetic ablation of CD11a, CD11b, CD11c or CD18 decreases the severity of inflammatory response in vivo in many experimental models [25-27]. However, such blocking agents have had little success in treating inflammatory/autoimmune diseases in humans [26, 28], perhaps because complete blockage of integrins with antibodies is difficult due to availability of a large mobilizable intracellular pool of such integrins (for example, CD11b/CD18) [29, 30] or because suppressing leukocyte recruitment with blocking agents requires occupancy of >90% of active integrin receptors [31]. Anti-integrin β2 antibodies have also shown unexpected side effects [32].
The above suggests that what is needed are small molecules that selectively regulate the ligand binding and function of beta2 integrins, including integrins CD11a/CD18 and integrin CD11b/CD18. Additionally, agents that do not compete with ligand binding (by targeting allosteric regulatory sites, such as the hydrophobic site-for-isoleucine (SILEN) pocket in CD11b/CD18) are especially desired. Moreover, compounds and methods to enhance or promote integrin-mediated cell-adhesion are highly desired. Furthermore, compounds that regulate cellular functions (such as cell activation and signaling) of inflammatory cells are highly desirable. Integrin activation has been proposed as an alternative to blockade (anti-adhesion) for modulating cell function and treating a number of diseases, including inflammatory diseases [33, 34]. It is based on the initial finding by Harlan and co-workers over 15 years ago that freezing of integrin α4β1 in high avidity state using an activating antibody increases cell adhesion and decreases eosinophil migration [35]. Recent research with knock-in animals that express activating mutants of integrins αLβ2 [36, 37] and α4β7 [38] provides in vivo support for this hypothesis.
However, compounds that enhance integrin activity are highly desired but no integrin-specific compounds and methods have been previously described. Additionally, whether transient activation of a fraction of native receptors in vivo, as is expected from small molecule treatment, will have biological effect also remains an open question. Moreover, an important requirement of useful compounds and compositions that regulate beta2 integrins, including CD11b/CD18, is that they not negatively impact the cell, tissue and animal viability. Some have suggested that integrin agonists might induce killing of target cells (Yang et al., J Biol Chem 281, 37904 (2006)), which is not desirable. Also, there is some prior art on the thiazolidine-one family of compounds, including U.S. Pat. No. 5,225,426, U.S. Pat. No. 7,566,732, U.S. Pat. No. 7,348,348, US 2006/0281798, US 2006/0183782, US 2006/0106077, US 2008/0108677, US 2010/0056503, WO 2009026346, WO/1995/029243. However, no compounds or methods with above described desirable properties have so far been described in the literature. It is an object of the invention to describe such compounds and methods. In addition, the present invention provides other related advantages.